In many adhesive dispensing modules, the flow of adhesive material is controlled by a dispenser valve member that moves between open and closed positions. In these modules, the dispenser valves typically include pistons that are pneumatically actuated to move by pressurized air. It is important that the pistons responsible for controlling the flow of material move quickly and reliably between the open and closed positions. As such, it is desirable to increase the speed and accuracy of these pistons without adding unnecessary parts or expense.
In a typical air-actuated dispensing module, pressurized air is directed into a chamber above the piston in order to force the piston and valve into an open position. The air is evacuated during a return movement of the piston to close the valve. The return movement is generated by various methods, including but not limited to biasing with a return spring and directing pressurized air to the opposite side of the piston. When the air is redirected to the opposite side the piston, the same passages are generally used to deliver air into and out of the piston chamber. Such an arrangement therefore requires the use of a switching solenoid that is capable of reversing air flows. The necessary amount of time to shift the valve between open and closed positions increases as a result of the additional time needed by the solenoid to reverse operation and the additional time necessary to reverse flow in the same passages.
Moreover, the performance of current pneumatically actuated dispensing modules may be hindered by uneven air flow where the pressurized air enters and exits at one side of the piston chamber. The uneven air flow entering the piston chamber takes more time to fully pressurize the piston chamber to force the piston to move. In this regard, the uneven air flow further increases the necessary amount of time to shift the valve between open and closed positions.
There is a need, therefore, for a dispensing module having a pneumatic actuator that addresses one or more of these deficiencies in the field of dispensing modules and reduces the amount of time required to shift a dispenser valve member between open and closed positions.